FIG. 14 shows an example of a conventional plasma display panel (hereafter called “PDP”). This figure is a perspective view, partly in cross section, of an AC PDP.
As shown in this figure, the AC PDP is composed of a front panel 75 and a back panel 85 which are opposed to each other. The front panel 75 is formed with a plurality of pairs of a stripe-shaped scanning electrode 71 and a stripe-shaped sustaining electrode 72 which are placed in parallel on a transparent first glass substrate 70 (an insulate substrate) and are covered by a dielectric layer 73 and a protective layer 74. The back panel 85 is formed with a plurality of stripe-shaped data electrodes 81 which are placed on a second glass substrate 80 (an insulate substrate), extend orthogonally to the scanning electrodes 71 and sustaining electrodes 72, and are covered by a dielectric layer 82. A plurality of stripe-shaped partition walls 83 are placed in parallel on the dielectric layer 82 so as to be located above and between the data electrodes 81. Also, phosphor layers 84 in different colors are provided along sides of the partition walls 83.
A space formed between the front panel 75 and the back panel 85 is filled with an inert gas including one or more type of gases selected among He, Ne, Ar, Kr, and Xe as a discharge gas. In this space, a portion where the scanning electrode 71, the sustaining electrode 72, and the data electrode 81 intersect together constructs a light-emitting cell 90 (also referred to as a discharge space).
The scanning electrode 71 and the sustaining electrode 72 are made up of stripe-shaped conductive transparent electrodes 71a and 72a, and bus electrodes 71b and 72b which are formed on the transparent electrodes, are narrower than the transparent electrodes, and include Ag. The data electrode 81 also includes Ag.
This AC PDP operates as follows. In a period for sustaining a driving operation after initialization and an address period, a pulse voltage is alternately applied to the scanning electrode 71 and the sustaining electrode 72. Then, an electric field developed between the protective layer 74 on the scanning electrode 71 across the dielectric layer 73 and the protective layer 74 on the sustaining electrode 72 across the dielectric layer 73 generates a sustaining discharge in the discharge space 90. Ultraviolet rays from this sustaining discharge excite phosphors in the phosphor layer 84, which causes emission of visible light. This visible light forms an image on the panel.
Here, a method for forming the scanning electrode 71, the sustaining electrode 72, the dielectric layer 73, and the protective layer 74 on the first glass substrate will be briefly described. First, stripe-shaped conductive transparent electrodes 71a and 72a consisting of tin oxide or indium-tin oxide (ITO) are formed on the first glass substrate 70. Then, a photosensitive paste including Ag is deposited thereon, patterned according to photolithographic method, and baked to form stripe-shaped bus electrodes 71b and 72b including Ag. Then, a dielectric glass paste is printed thereon and baked to form the dielectric layer 73. After that, magnesium oxide (MgO) is deposited by evaporation to form the protective layer 74.
Next, a method for forming the data electrode 81, the dielectric layer 82, the partition wall 83, and the phosphor layer 84 on the second glass substrate will be briefly described. First, a photosensitive paste including Ag is deposited on the second glass substrate 80, patterned according to a photolithography method, and baked to form stripe-shaped data electrodes 81 including Ag. Then, a dielectric glass paste is printed thereon and baked to form the dielectric layer 82. After that, the partition walls are formed according to a screen-printing method, a photolithography method, or the like, and the phosphor layers 84 are formed according to a screen-printing method, an ink-jet method, or the like.
Then, a glass member for seal is inserted between the peripheral portions of the front panel 75 and the back panel 85, and this glass member is fused and cooled so as to seal the both substrates. After that, exhausting and gas filling processes are conducted to complete the panel.
As stated above, the bus electrodes 71b and 72b and the data electrodes 81 are formed according to the photolithography method using an Ag photosensitive paste. The following describes these processes in detail using figures. FIG. 15 shows manufacturing processes in the photolithography method. In this figure, the method is explained by showing an example of the front panel.
First, ITO is deposited by evaporation onto the first glass substrate 70. Then, an Ag photosensitive paste is applied according to a printing method or the like to form an Ag photosensitive paste layer 100 (FIG. 15A). Next, a drying process is performed in order to drive off a solvent included in the Ag photosensitive paste layer 100.
Next, the layer 100 is exposed to ultraviolet radiation through a photolithographic mask 102 to form exposed regions 103 and unexposed regions 104 (FIG. 15B). This exposed regions serve as patterns of the bus electrodes in the finished products.
Next, a development process is performed to fix the exposed regions on the first glass substrate 70 (FIG. 15C). These fixed portions in the development process are referred to as a pre-baking electrode structure 105.
Next, the pre-baking electrode structure 105 is baked into the bus electrodes (FIG. 15D). In this process, the pre-baking electrode structure 105 is reduced in the size as can be seen from the comparison between FIGS. 15C and 15D (Note that these figures are slightly exaggerated in their size for purposes of illustration).
In this way, a patterning process according to the photolithographic method using the Ag photosensitive paste is necessarily accompanied by the baking process in order to drive off a resin component in the paste. This process, however, has given rise to a problem of “edge curl phenomenon”. It can be thought that this phenomenon mainly results from the action of the tensile force generated by heating.
FIG. 15D includes an enlarged view of the bus electrodes, which shows this edge curl phenomenon. The edge curl phenomenon, as shown in this figure, is a state where both sides of the pre-baking electrode structure 105 for the bus electrodes are warped upward against the first glass substrate after the baking process. When this phenomenon occurs, it becomes difficult to form the dielectric layer on the portions, and the dielectric layer formed on the portions becomes susceptible to an electrical breakdown because the portions have sharp edges. To address the problem, the edge curl portions of the post-baked bus electrodes and data electrodes may be ground away.
Meanwhile, in case that the bus electrodes provided on the front panel are formed using a substance including Ag as above, incident light is reflected by the bus electrodes due to a relatively large reflectivity of Ag, which remarkably deteriorates a contrast in the image on the panel. To cope with this problem, an optically double-layered structure in which a black-white multiple layer and a white layer is laminated has been in practical use as the bus electrodes provided on the front panel. In this structure, the multiple layer configured so that a metal layer including a black pigment and a metal layer including Ag are laminated (“black-white multiple layer”) is formed on the first glass substrate, and an Ag metal layer of low resistance (“white layer”) is formed thereon.
This double layered bus electrodes are also formed according to the photolithographic method as shown in FIGS. 16A to 16F in the same manner as in the above single layer.
That is, as shown in FIG. 16A, a photosensitive paste including a black pigment is applied to form a printed layer 110. Next, a drying process is performed to drive off a solvent from the printed layer 110.
Next, as shown in FIG. 16B, an Ag photosensitive paste is applied to the surface of the printed layer 110 to form a printed layer 111. Next, a drying process is performed to drive off solvents from the printed layers 110 and 111.
Next, as shown in FIG. 16C, these layers are exposed to ultraviolet radiation through a photolithographic mask 113 to form exposed regions 114 and unexposed regions in the printed layers 110 and 111. These exposed regions serve as patterns of the black-white multiple layer in the finished products.
Note that the above FIGS. 16A to 16C are slightly exaggerated in their film thicknesses or the like for the sake of clarity.
Next, a development process is performed to fix the exposed regions 114 on the first glass substrate 70 (FIG. 16D).
Next, a layer configured as lamination of a layer 116a including the black pigment and a layer 116b including Ag is baked into a black-white multiple layer 116 (FIG. 16E).
Next, as shown in FIG. 16F, a white layer 117 is applied according to a photolithographic method, a screen-printing method, or the like and baked to complete the bus electrodes.
As shown in the cross-sectional view, the black-white multiple layer in the process of FIG. 16E has the edge portions which are warped upward (“edge curled”) so that a concave portion 116c is formed at the top of the layer. Then, an Ag photosensitive paste is selectively applied to the concave portion 116c according to a photolithographic method, a screen-printing method, or the like, and this structure is baked again. As a result, as shown in FIG. 16F, a top surface of the electrode becomes flat in the finished bus electrode, so that an influence by the edge curl phenomenon in the black-white multiple layer can be substantially avoided.
This method provides advantages that an influence by the edge curl phenomenon can be substantially avoided as described above. However, a demand for a matter of convenience by performing the baking process only once cannot be satisfied by the above method.